1. Field of the Invention
The present invention relates to an ESD protection device to protect a semiconductor device or other electronic devices from electrostatic discharge failures and a method for manufacturing a ESD protection device.
2. Description of the Related Art
In recent years, in commercial-off-the-shelf appliances, there has been an increase in the frequency of inserting and removing cables as input-output interfaces, and static electricity is likely to be applied to input-output connector areas. In addition, miniaturization in design with an increase in signal frequency has made it difficult to create paths, and large-scale integration (LSI) itself has been fragile to static electricity.
Therefore, ESD protection devices have been used widely for protecting semiconductor devices, such as LSI devices, from electrostatic discharge (ESD).
As this type of ESD protection device, an ESD protection device (chip-type surge absorber) including an insulating chip body which includes an enclosed space with an inert gas encapsulated in the center, opposed electrodes which each has a microgap in the same plane, and external electrodes, and a method for manufacturing the ESD protection device have been proposed (see, for example, Japanese Patent Application Laid-Open No. 9-266053).
However, in the ESD protection device (chip-type surge absorber) in Japanese Patent Application Laid-Open No. 9-266053, electrons need to jump directly across the microgaps of the opposed electrodes without any assistance, and thus, the discharge capacity of the ESD protection device depends on the widths of the microgaps. Furthermore, as the microgaps are narrowed, the capacity as a surge absorber is increased. However, the width of a gap is limited by the formation of opposed electrodes using a printing method as described in Japanese Patent Application Laid-Open No. 9-266053, and an excessively narrow gap results in problems, such as the opposed electrodes connected to each other to cause a short circuit.
In addition, as described in Japanese Patent Application Laid-Open No. 9-266053, a hollow section is provided by stacking perforated sheets. Thus, considering that there is a need to provide a microgap in the hollow section, the reduction in size of the product also is limited in terms of stacking accuracy. Furthermore, in order to provide the enclosed space filled with an encapsulating gas, there is a need to perform stacking and pressure bonding under the encapsulating gas for stacking, thus leading to the problems of a complicated manufacturing process, a decrease in productivity, and an increase cost.
Furthermore, as another ESD protection device, an ESD protection device (surge absorbing element) provided with internal electrodes electrically connected to a pair of electrodes and a discharge space within an insulating ceramic layer including the external electrodes, and with a discharge gas trapped in the discharge space, and a method for manufacturing the ESD protection device have been proposed (see, for example, Japanese Patent Application Laid-Open No. 2001-43954).
However, the ESD protection device in Japanese Patent Application Laid-Open No. 2001-43954 also has the same problems as in the case of the ESD protection device in Japanese Patent Application Laid-Open No. 9-266053.
In addition, as yet another ESD protection device, an ESD protection device including a ceramic multilayer substrate, at least a pair of discharge electrodes provided in the ceramic multilayer substrate and opposed to each other with a predetermined distance provided therebetween, and external electrodes provided on the surface of the ceramic multilayer substrate and connected to the discharge electrodes has been proposed in which a region for connecting the pair of discharge electrodes includes an auxiliary electrode obtained by dispersing a conductive material coated with a nonconductive inorganic material (see, for example, Japanese Patent No. 4434314).
However, this ESD protection device has a problem in that a glass component in the ceramic multilayer substrate penetrates into the discharge auxiliary electrode to make the conductive material of the discharge auxiliary electrode excessively sintered during a firing step for the manufacture of the ESD protection device, thereby causing a short circuit defect.